This invention belongs to the field of the treatment of flat, absorptive, compressible web materials with liquids such as treating liquor or finishing baths. In particular, the invention relates to a method for the continuous application of liquors, especially finishing liquors, on absorptive and compressible material webs, in particular fibrous webs such as textile webs, which are made to advance in a continuous and uniform manner from a supply, e.g. a spool, to a winding-on device or equivalent.
This invention is also related to apparatuses for carrying out the method.
The following description makes reference to the general case where advancing textile fiber webs are concerned. However, other absorptive, compressible webs may be substituted therefore such as certain papers spongeous materials, synthetic and natural fiber fleeces, etc to which this invention also applies.
The instant invention refers to a method wherein such amounts of liquor are applied in one or several steps that the maximum amount of liquor which the web can take up by absorption, called the absorptivity limit, is not reached but where those amounts are greater than the water retention value of the web. The water retention value is a physical property of the web and may be determined by the DIN standard no. 53'814 (ASTM-D2402-65T). Processes where the absorptivity limit is reached and the liquor excess is removed afterwards, thus in particular the pad mangle methods, are outside the scope of this invention.
Quite a number of methods and working techniques are known in the textile processing art which are used to apply liquors of treating bathes to textile fiber webs. The term "web" comprises, in a known manner, a textile substrate which may absorb liquids, whose length is very great compared to its width, e.g. by about 500 to 10,000 times, and whose thickness is comprised between one and about ten times the diameter of the constituting fiber. This term "web" therefore comprises, besides the woven fabrics, also knitted fabrics and other non-woven webs such as vleeces. It further comprises rows or layers of parallel warp yarns which are to be sized, bleached or dyed before weaving. In these cases, the overall thickness of the web may even be greater.
Examples of such techniques are the padding, the kiss roller application, the different methods of impregnation, the spraying, the application of liquors with sponges, the application of foamed liquors and the printing. In many cases, it is necessary or appropriate to apply first an excess of liquor and to remove that excess afterwards. An important example of the latter method is the pad mangle where the textile web is offered as much liquor as it may take up, and any excess is removed between squeeze rollers. It is not possible to remove any liquor in excess over the above-mentioned water retention value. Using technically reasonable squeezing pressures, the amount of liquor remaining in the web after squeezing is higher than that value. Without squeezing, the applied amount of liquor called "pickup" cannot be metered or controlled.
An important process for the application of liquors, especially of treating liquors, on textile webs is a method introduced in the '70s and called "MA process" (MA stands for minimum application) which brings about a uniform, controlled impregnation without local or overall excess application of liquors on textile material webs under high working speeds. It is disclosed, for example, as well as a preferred apparatus for its implementing, in U.S. Pat. Nos. 3,862,553 and 3,822,834. It does not comprise any squeezing device. The minimum application amount is defined as that liquor amount in % by weight which is in the range between zero and a value given by the expression (W.sup.2 /150)+40 wherein W is the above defined water retention value. The upper limit of the amount of applied liquor, defined by the above-indicated expression, is situated at about 10 to 30% by weight of the limit of the squeezable excess. The process has found world-wide application and introduction, it is well known to the people skilled in the art, and it is deemed unnecessary to mention its advantages herein.
Although the process just mentioned has been known as a "minimum application" method, it may also be used to apply greater amounts of liquors in a metered, controlled and uniform manner. This alternative and generalized technique is named in the following as "metering roller application" and comprises the minimum application as well. This metering roller application technique therefore comprises all applications resulting in applied amounts between the value of W and the saturation value (absorption limit) of the substrate.
The application of about 10 to 25% by weight of preferably aqueous liquors on dry hydrophilic textile webs, i.e. webs containing not more than about 15% by weight of natural or residual humidity, is easy in that a uniform one-side application will be homogeneously spread and distributed throughout the textile material due to capillary forces. However, it may happen even in the minimum application method that particularly weakly fiber affine and viscous liquors will give an uneven or undesirably one-sided application result.
In the case of greater application quantities, the time duration available for the homogeneous distribution of the applied liquor in the material web which is given by the dwell time of the web between the applicator device and the drying means, will sometimes not be sufficient so that inhomogenities are observed. Similar phenomena occur when the web to be loaded with a liquor already contains another one; in this case, the uneven liquor distribution is even more significant since the liquor distribution within the web material is based here essentially on liquid-liquid diffusion, a process which is significantly slower than a distribution by capillarity.
A uniform liquor or bath distribution in the cases just discussed has been achieved until now by dwelling techniques where the web is wound up and abandoned for a longer time. Dwelling techniques, however, are material, space and capital consuming.
Another approach to achieve a uniform liquor distribution are the pad mangle techniques which do not, however, belong to the instant field of invention. Further advantages of this approach, besides the already mentioned limitation in application control, are expensive machinery, technically complicated operation and the fact that, when webs already containing a liquor are used, this liquor is partially squeezed out together with the impregnation second liquor.
It has already been suggested to pass a sizing liquor containing web formed by rows of parallel and horizontal warp yarns through a squeezing device having squeezing rollers. It is not known whether an equalizing of the sizing liquor may be obtained; anyway the mere squeezing is a uncontrolled operation, and generally part of the sizing liquor is squeezed out of the warp yarns which is not desired.
Swiss patent specification no. 530,230 casually mentions that the uniform impregnation of a textile material by a finishing liquor may be enhanced at particularly adverse conditions by special measures such a mechanical means. However, this reference exclusively deals which the minimum application defined above where, in detrimental cases of the liquor distribution, the use of squeezing means may accelerate this distribution. Experiments have nevertheless shown that the uniformity of distribution is a feature characteristic for the minimum application, and thus the use of squeezing means could not give a model to cases where there is a squeezable liquor excess in the web material.
Squeezing devices are composed of at least one pair of cooperating rollers; at least one roller of the pair is provided with a rubber elastic surface or is totally made from rubber. The material web is passed between the rollers and pinched by them. A squeezing effect is obtained in that the two rollers are pressed against each other, the elastic surface of the rubber roller flattens in the contact region, and exerts a squeezing action. An adjustment of the squeezing effect is, as in the pad mangle, only possible in very narrow limits. It has been found that such a squeezing device is not fitted for the invention and cannot be used.